Definitions_Only

Question 1

Amount

Answer 1

A measure used by chemists for counting particles; the unit is the mole

Question 2

Avogadro’s number

Answer 2

The umber of particles in a mole; symbol N_A = 6.02 x 10²³ mol^-1

Question 3

carbon-12

Answer 3

The isotope of carbon that has a mass number of 12. The isotope contains 6 protons and 6 neutrons. One atom of carbon-12 is taken as having amss of exactly 12 units. This is the standard from which all other relative masses are calculated

Question 4

empirical formula

Answer 4

A formula that shows the simplest whole number ration of the elements in a compound. Eg CH is the empirical formula of propene (C₃H₆)

Question 5

formula

Answer 5

A representation of an element or copound using symbols for its constituant elements. It shows the ration of atoms in a compound or the number of atoms in a molecule

Question 6

ionise

Answer 6

The reaction of a molecular substance with a solvent to form ions in solution. When some polar molecules dissolve in water they ionise to form a hydronium ion. Eg: HCI(g) + H₂O(I) ->H₃O⁺(aq) + CI^-(aq)

Question 7

isotope

Answer 7

Each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei. Eg: ¹²C and ¹³C are isotopes of carbon.

Question 8

mass spectrometer

Answer 8

An instrument that measures the mass-to-charge ratio of particles.

Question 9

mass spectrum

Answer 9

A plot of the isotopic mass, relative to the mass of carbon-12 taken as 12 units exactly, against the relative abundance of each isoptope present in a sample.

Question 10

molar mass

Answer 10

The mass of one mole of a substance measured in

g mol^-1; symbol M.

Question 11

mole

Answer 11

The amount of substance that contains the same number of fundamental particles as there are atoms in 12 g of carbon-12; symbol n; unit mol.

Question 12

molecular formula

Answer 12

A formula of a compound that gives the actual number and tupe of atoms present in a molecule. It may be the same as or different from the empirical formula.

Question 13

molecule

Answer 13

A group of two or more atoms covatently bonded together, and represting the smallest fundamental unit of a chemical compound.

Question 14

percentage composition

Answer 14

The proportion by mass of the different elements in a compound.

% by mass of an element in a compound = mass of the element present / total mass of the compound x 100

Question 15

relative atomic mass

Answer 15

The weighted average of the relative isotoic masses of an element on he scale where ¹²C is 12 units exactly.; Symbol A_r.

Question 16

relative formula mass

Answer 16

The mass of a formula unit relative to the mass of an atom of ¹²C taken as qw units exactly It is numerically equal to the sum of the relative atomic masses of the atoms making up the formula. Substances that contain atoms or ions bonded in lattice structures have a relative formula mass. Such compounds include ionic compounds and covalent network substances.

Question 17

relative isotopic abundance

Answer 17

The percentage abundance of a particuar isotope in a sample of an element.

Question 18

relative isotopic mass

Answer 18

The mass of an atom of the isotope relative to the mass of an atom of carbon-12 taken as 12 units exactly

Question 19

relative molecular mass

Answer 19

The mass of a molecule relative to the mass of an atom of ¹²C, taken 12 uints exactly; Symbol M_r

Question 20

Reactant

Answer 20

A substance that takes part in and undergoes change during a reaction.

Question 21

Limiting Reactant

Answer 21

Reactant is completely consumed

Question 22

Excess Reactant

Answer 22

The reactant is not completely consumed

Question 23

Stoichiometric

Answer 23

relating to or denoting quantities of reactants in simple integral ratios, as prescribed by an equation or formula.